The present invention relates to a molded case circuit breaker, and in particular, to an assembly structure of a current-interrupting section equipped with a bridging rotary contact shoe.
First, a general configuration of a molded case circuit breaker is schematically shown in FIG. 7. In this figure, reference numeral 1 denotes a main body case of a circuit breaker, 2 is an opening and closing handle, 3 is a toggle type opening and closing (switching) mechanism, and 4 is an over-current tripping device based on a bimetal method or the like. Reference numeral 5 is a current-interrupting section containing fixed contact shoes, a movable (rotary) contact shoe and arc extinguishing devices of a main circuit, and is linked to the opening and closing mechanism 3. An opening and closing operation of such a circuit breaker is well known.
Through an ON/OFF operation of the opening and closing handle 2, the movable contact shoe in the current-interrupting section 5 opens or closes via the opening and closing mechanism 3. Further, when an over-current flows to activate the over-current tripping device 4 while the main circuit is powered, the opening and closing mechanism 3 performs a trip operation to open the movable contact shoe in the current-interrupting section 5, thereby interrupting the over-current from flowing through the main circuit.
Here, an interrupting method used for the current-interrupting section 5 includes a single-break method and a double-break method. An example of a double-break method using a bridging rotary contact shoe as a movable contact shoe has been disclosed in Japanese Patent Publications (KOKAI) No. 06-028964 and No. 06-52777. A configuration of this circuit breaker is shown in FIG. 8. In this figure, reference numeral 6 denotes an insulated case of the current-interrupting section 5; 7A and 7B are power-supply side and load side fixed contact shoes disposed in the insulated case 6 and arranged diagonally opposite to each other; 7a is a fixed contact provided at a tip portion of each fixed contact shoe; 8 is a movable contact shoe that bridges the contacts of the fixed contact shoes 7A, 7B; 9 is a rotary drum-shaped contact shoe holder that holds the movable contact shoe 8; and 10 is an arc extinguishing device (grid) positioned at each side of the movable contact shoe 8 and disposed in the insulated case 6.
The movable contact shoe 8 is urged and held in a position by a pressure spring (tension spring or torsion coil spring) 11 loosely fitted and disposed in a through-hole 9a formed on the contact shoe holder 9. One end of the fixed contact shoe 7A (a power-supply side) is drawn out from the insulated case 6 to constitute a power-supply-side terminal portion. A terminal portion of the fixed contact shoe 7B (a load side) is connected to the main circuit conductor of the overload tripping device 4, shown in FIG. 4, at a top surface of the insulated case 6.
Further, in the illustrated structure, a tip portion of each of the fixed contact shoes 7A and 7B is folded in a U-shape to form a fixed contact 7a. When an over-current such as a short circuit current flows through the main circuit, the movable contact shoe 8 is substantially instantaneously opened before the overload tripping device 4 (see FIG. 7) operates by an electromagnetic resilient force exerted between the tip portions of the fixed contact shoes 7A and 7B and the movable contact shoe 8. Furthermore, the folded portion of each fixed contact shoe has a magnetic yoke 12 to enhance a magnetic field acting on an arc generated between the contacts of the fixed and movable contact shoes during current interruption, thereby increasing the electromagnetic arc driving force to the arc extinguishing devices 10.
It is preferred for the current-interrupting section 5 to be as compact as possible in order to reduce a size of the molded case circuit breaker. However, in the conventional structure of the current-interrupting section shown in FIG. 8, the tip portion of each of the power-supply side and load side fixed contact shoes 7A and 7B is folded in the U-shape to generate the electromagnetic resilient force required to drive and open the movable contact shoe 8 when the over-current flows through the circuit. As a result, the insulated case 6, which contains the fixed contact shoes 7A and 7B, needs to have a larger height H, resulting in a larger size of the current-interrupting section 5.
Further, as shown in FIG. 9, Japanese Patent Publication (KOKAI) No. 01-166429 has disclosed a molded case circuit breaker in which the fixed contact shoes 7A and 7B, disposed in the insulated case 6 of the current-interrupting section 5 and arranged diagonally opposite to each other, are formed of linear contact shoe conductors. The bridging rotary contact shoe 8 is disposed between the fixed contacts 7a provided at the tips of the fixed contact shoes 7A and 7B. In this assembly structure, the fixed contact shoes 7A and 7B in the insulated case 6 have a linear shape, thereby allowing the height H of the current-interrupting section 5 to be smaller as compared to the configuration in FIG. 8. On the other hand, a current direction flowing through the fixed contact shoes 7A and 7B is the same as that through the movable contact shoe 8. Therefore, a large electromagnetic resilient force required for driving and opening the movable contact shoe can not be obtained between each of the fixed contact shoes 7A and 7B and the movable contact shoe 8.
It is thus an object of the present invention to provide a molded case circuit breaker having linear shape fixed contact shoes to minimize a current-interrupting section, wherein the contact shoes are arranged so as to generate a large electromagnetic resilient force required for driving and opening a movable contact shoe when an over-current flows through the circuit.
Further objects and advantages will be apparent from the following description of the invention.
To achieve the objects, the present invention provides a molded case circuit breaker including a current-interrupting section. The current-interrupting section is composed of an insulated case containing arc extinguishing devices; fixed contact shoes on a power-supply side and a load side disposed in the case and arranged diagonally opposite each other; a movable or rotary contact shoe bridging between contacts of the fixed contact shoes; and a rotary contact shoe holder for holding and linking the movable contact shoe and a pressure spring to an opening and closing mechanism of the circuit breaker. The movable contact shoe can be opened by an electromagnetic resilient force exerted when an over-current flows. Contact shoe conductors of the power-supply side and load side fixed contact shoes are substantially linear, and are arranged in parallel and opposite to each other with the movable contact shoe in between. The fixed contact shoes, and the movable contact shoe which is bridging contacts positioned at tips of the fixed contact shoes, are assembled together to form a Z-shape conducting path (the first aspect).
According to this configuration, the fixed contact shoes are composed of linear contact shoe conductors, thereby reducing a height of the current-interrupting section as opposed to the conventional structure having a U-shape fixed contact shoe. Further, when the circuit breaker is powered, a current through the power-supply side and load side fixed contact shoes flows relatively opposite to that through the bridging movable contact shoe. Accordingly, if an over-current flows through the circuit, a large electromagnetic resilient counter force is generated between a tip portion of the power-supply side fixed contact shoe and the movable contact shoe, and between the tip portion of the load side fixed contact shoe and the movable contact shoe. This electromagnetic counter force acts as a driving torque to drive and open the movable contact shoe.
Further, according to the present invention, to further improve the opening operation of the movable contact shoe and the interrupting performance, the following specific approaches are implemented in addition to the above configuration.
A magnetic yoke is disposed in an area around the tip portion of each of the power-supply side and load side fixed contact shoes, thereby enhancing the magnetic field acting on the movable contact shoe to increase the electromagnetic counter force. Further, magnetic field acting on an arc generated between the contacts of the fixed and movable contact shoes during current interruption is enhanced to increase an electromagnetic arc driving force directing to the arc extinguishing devices (the second aspect).
The tip portion of each of the power-supply side and load side fixed contact shoes is tilted relative to the movable contact shoe, so that the electromagnetic resilient or counter force generated between the tip portions and the movable contact shoe acts effectively as a driving torque required to rotate the movable contact shoe around its rotational center (the third aspect).
The tip portion of each of the power-supply side and load side fixed contact shoes is set to be narrower than the conductor thereof, which is located behind the tip portion thereof, thereby concentrating a current to strengthen the magnetic field generated in a peripheral area of the tip portions to increase the electromagnetic resilient force acting on the movable contact shoe. In this case, the conductor portion of the contact shoe, which is wider than the tip portion, absorbs and dissipates heat generated at the contact portion as a result of the current interruption to prevent over-heating of the terminal portion of the fixed contact shoe located at the rear end thereof (the fourth aspect).
A magnetic shielding member is provided at an area near each of the tip portions of the fixed contact shoes facing each other with the movable contact shoe in between. This configuration prevents a magnetic field that is applied to the movable contact shoe to rotate in a closing direction of a rotational path of the movable contact shoe (the fifth aspect).
Each of the fixed contact shoes may have a slit at an area near the tip portion thereof facing each other along a longitudinal direction of the contact shoe conductor thereof, and the slit divides the conductor into two lateral portions. The magnetic field generated in a peripheral area of each conductor is dispersed so as to suppress the electromagnetic resilient force acting toward a closing direction of the movable contact shoe (the sixth aspect).
A hot gas discharge port may be provided on each of power-supply side and load side ends of the insulated case of the current-interrupting section. The discharge port has an opening perpendicular and opposite to the contact shoe conductors of the fixed contact shoes drawn out from the insulated case. Consequently, a hot gas generated in the insulated case of the current-interrupting section by the arc generated when a large current is interrupted is prevented from blowing directly against the conductor of each fixed contact shoe drawn out from the insulated case and its periphery, which results in an inter-pole flashover (the seventh aspect).
The terminal portion of the fixed contact shoe laid along a bottom surface of the insulated case is bent in a U-shape and drawn out from an end surface of the insulated case. The magnetic field generated in a periphery of the terminal portion as a result of a current flowing through the contact shoe conductor is prevented from inhibiting extension of an arc generated between the fixed and movable contacts during current interruption, thereby ensuring higher interrupting performance (the eighth aspect).